Items of seating furniture, especially armchairs, that permit motor-aided adjustment of the backrest and the seat are known from practice. By means of a control system, the user can adjust the item of seating furniture continuously between a relatively upright position and a reclined position.
U.S. Pat. No. 4,834,454 discloses an office chair with tiltable seat and back. A lever, swingably mounted to the chair, responds to the specific weight of the user to carry the chair's back forwardly to comfortably support the back of the user without any required adjustment. The seat and the back move simultaneously but in different directions, because the lower arm of the lever pushes the seat upwardly as the chair back is tilted rearwardly.
The operating mechanism usually has an electrical motor which brings about the adjustment of the seat and the backrest by way of a linkage. The user finds it more pleasant when the angle between the seat and the backrest in the reclined position is larger than in the sitting position. In order to bring about this sequence of movement with a single drive motor, relatively complex linkages are provided between the motor, the seat and the backrest in the items of seating furniture known from practice. Those linkages are relatively complex both in terms of manufacture and in terms of assembly. In addition, they require a relatively large amount of installation space, so that such items of seating furniture often appear relatively bulky and unattractive. Although a correspondingly thinner upholstery material could be used, that would lead to an undesirable loss of comfort.